Cairn et Tumulus d'Er Grah and Le Grand Menhir Brisé

These are two of the most impressive megalith monuments in Locmariaquer. Er Grah used to be much bigger, but stones were taken away from the cairn, to be used elsewhere. The chamber is covered with a big rock, and it's not possible to enter it. The big broken standing stone that is lying down in four separate pieces just south of Er Grah. In one piece it used to be
20.60 metres (67.6 ft) and weigh 330 tons. Read more about it on Wikipedia.

The foundation where the Grand Menhir Brisé used to stand is marked out with small stones in a circle, and there's also 18 more markings like this in a row, right next to each other, which mean that there were once 19 menhirs standing in an alignment on this site. According to the Wikipedia-link above, there was probably an earthquake that made the menhir fall, and then the people used the other 18 stones as building material for several other monuments, like Dolmen de la Table des Merchands.